Floor lighting arrangements have been proposed, for example based on a circuit board carrying an array of LEDs, for example with a pitch of 12.5 mm. A robust and stiff frame is needed around and over the LED printed circuit boards in order to allow a user to stand over the location of the LED lighting.
Such a frame cannot span the size of a floor area whilst maintain a desired rigidity, so it needs to be formed as an array of frame members. The frame must carry the same loads as a standard floor.
One cost effective solution for the frame design is to provide a folded sheet metal frame, with folded edges all around which bend down towards to the underlying supporting structure, such as a floor. The frame then provides a suspended surface beneath which the LED PCB can be mounted. Openings in the suspended surface enable the LED light to escape and to be projected upwardly.
From an aesthetic point of view, it is desirable to enable a continuous LED pitch across the floor area. The two folded edges which butt together at the join between the frame members have a width of double the material thickness of the frame member. This limits the lowest value of the achievable pitch between LEDs while maintaining a uniform pitch across of the overall area.
CN-101509622 discloses a floor lighting arrangement in the form of a LED display structure. The display structure comprises a circuit board provided with LEDs, and fixed to this circuit board, a bottom case with through holes at locations corresponding to those of the LEDs. Provided over the bottom case is a cover layer having blind holes at locations corresponding to those of the through holes in the bottom case. One such display structure can be connected to another by a latching means that is provided at the sides of the bottom case. The latching means consist of ribs and slots that are shaped such that the ribs of one display structure fit into the slots of another.
EP 1662068 discloses a modular floor design using floor tiles having bent flanges to support the tiles.
The design suffers the problem that to realize the robustness and stiffness, there is a limit to how closely the internal LED array circuits can be brought together. For example, in most situations the sheet metal thickness may be in the range 2.5 mm-3 mm, and this gives a 5 mm to 6 mm space between frame members, not including an additional bend radius of the sheet metal frame member and also a minimum edge dimension between the edge of the PCB and the LEDs at the LED edge.
The design thus limits the ability to reduce the LED pitch, which may be desired either to give a more uniform output or to enable a required light intensity to be achieved.